X-ray diffraction is a non-destructive technique for the qualitative and quantitative analysis of crystalline material samples, which are generally provided in the form of single crystals or powders. In accordance with this technique, an X-ray beam is generated by an X-ray tube with a stationary anode, by a conventional rotating anode X-ray source or by a synchrotron source and directed toward the material sample under investigation.
When the X-ray beam strikes the sample, the X-rays produce Bragg angle reflections from the parallel and equally spaced atomic planes in the crystalline substance. Diffraction occurs if the path of the X-rays reflected by successive planes is a multiple of the X-ray wavelength. Therefore, the spacing between the atomic planes of a crystal can be determined by detecting the diffracted X-rays and measuring the first-order angles of diffraction. These measurements are usually performed by rotating the crystalline sample while taking diffraction measurements. The resulting pattern is called a diffractogram. Texture or crystal structure analysis can be performed on the sample by applying standard techniques to the series of diffractograms obtained from the sample.
A device called a “goniometer” is used to position and hold the various components of the X-ray diffraction system. The goniometer has multiple moveable arms or fixed dovetail mounts on which the X-ray source (or, for synchrotron sources, the X-ray optics), the sample and an X-ray detector are mounted. In order to acquire the diffraction data, the sample is typically rotated by a stepper or servo motor. FIG. 1 illustrates a typical diffractometer 100 used for diffraction measurements of a single crystal. The diffractometer 100 is built on a goniometer base 102 having stages 104 and 106 that rotate around two concentric main rotation axes ω and 2θ. The stage 104 rotating around the 2θ rotation axis is used to support and position the detector 108 through the attached detector track 110. The x-ray source/optics 112 and collimator 114 is mounted on another track 116 attached to the goniometer base 102. The stage 106 rotating around the ω rotation axis is used to rotate the sample on the sample stage 118 relative to the incident X-ray beam from the collimator 114 and the detector 108. The sample stage 118 is the φ rotation stage which is used to rotate the single crystal sample. The φ rotation axis intersects the ω rotation axis at point C with a fixed angle χ between the two axes. The point C is referred to as the instrument center.
During a typical experiment, a single crystal sample 122 is mounted on the φ rotation axis by means of the goniometer head 120, which may additionally contain three orthogonal translation adjustments and/or tilt adjustments. The function of the goniometer head 120 is to bring the mounted single crystal sample 122 into the instrument center so that the incident X-ray beam through the collimator 114 strikes the sample 122 at the instrument center C and the sample stays in the instrument center while rotating about the φ axis and/or the ω axis. Some systems have a third sample rotation axis either as χ axis in Eulerian geometry or κ axis in kappa geometry.
However, since most single crystal samples are very small in size, typically a few hundred microns to a millimeter, a diffractometer dedicated for single crystal X-ray diffraction such as that shown in FIG. 1 cannot handle a large bulky sample or multiple samples. In order to handle large or bulky samples, the diffractometer must have a different construction. FIG. 2 illustrates a typical diffractometer 200 used for general X-ray diffraction for large samples and multiple samples. The system is built on the same goniometer as the system shown in FIG. 1 and corresponding parts have been given corresponding numeral designations. The goniometer base 102 contains two concentric main rotating stages 104 and 106. The stage 104 rotates around the 2θ rotation axis and supports and positions the detector 108 via the attached detector track 110. The x-ray source/optics 112 and collimator 114 are mounted on another track 116 attached to the goniometer base 102.
The stage 106 that rotates around the ω rotation axis is attached to the sample stage 206 via an arm 202 and rotates the stage 206 relative to the incident X-ray beam and detector. The XYZ stage 204 is used to hold large samples or multiple samples. The ω rotation axis intersects with the incident X-ray beam at the instrument center C and the XYZ stage 204 can bring a measuring spot on a large sample or multiple samples into the instrument center C. For certain experiments, the XYZ stage 204 may be replaced by a large Eulerian cradle with XYZ translations and rotations around the ψ and φ axes in Eulerian geometry. Since this diffractometer is dedicated to handling large samples and multiple samples, it lacks a sufficient rotation range for single crystal diffraction.
Existing X-ray diffractometers are designed either for single crystal X-ray diffraction or general diffraction with powder samples, bulky samples or multiple samples. However in some X-ray diffraction laboratories, a diffractometer suitable for both single crystal diffraction and general diffraction may be necessary. One example is a diffraction system that will be used both for single crystals and for samples under high pressure in a diamond anvil cell (DAC). Due to the heavy weight and bulky size of the DAC, a motorized XYZ stage is necessary to hold and automatic align the sample. One solution is to replace the φ rotation stage 118 shown in FIG. 1 by the XYZ stage 204 shown in FIG. 2. However, reinstalling the φ rotation stage 118 and realigning the φ axis into the instrument center after each use of the XYZ stage 204 is a tedious job and may require a trained person with a set of special tools.